In power supply circuitry it is desirable to design the rectifier diodes such that when they are in the xe2x80x98onxe2x80x99 state, they possess a very small forward voltage drop and when they are switched rapidly to the xe2x80x98offxe2x80x99 state, they do so without ringing. Additionally the rectifier diodes must be designed to have the required breakdown voltage. Unfortunately designers have found it difficult to design rectifier diodes with all of the desired characteristics. For example, germanium based diodes, regardless of whether they are PIN or Schottky structures, exhibit a low turn-on voltage relative to silicon diodes due to their small bandgap. On the other hand, gallium arsenide based diodes, which have a relatively high turn-on voltage due to their large bandgap, exhibit high current density relative to either silicon or germanium due to their high mobility and are capable of rapid switching without ringing.
Accordingly, what is needed in the art is a rectifier structure that has a low turn-on voltage and can be rapidly switched without ringing. The present invention provides such a structure.
The present invention provides a rectifier structure that exhibits a low turn-on voltage while allowing rapid switching without ringing. According to the invention, a thin epitaxial layer is interposed between the two layers that comprise the rectifier junction. Preferably the epitaxial layer is of the same conductivity as the underlying layer while being comprised of the same material as the outermost layer. As the layer is epitaxially grown, preferably the lattice of the material comprising the layer is a close match to that of the underlying layer, thus allowing the as-grown layer to be of high quality.
The present invention can be used with a variety of semiconductor material pairs, in particular material pairs in which one member has a relatively small bandgap and the other member has a relatively high mobility. As the smaller bandgap material sets the maximum field for the device, typically devices fabricated in accordance with the present invention are primarily useful in low voltage applications.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.